The present invention is directed to bicycles and, more particularly, to a circuit for controlling power from a dynamo.
Bicycles are typically equipped with a dynamo that provides power for lighting a lamp, such as a headlamp. Devices for controlling lamp operation are disclosed, for example, in Japanese Unexamined Patent Application 5-238447 and Unexamined Patent Application 2000-62523. According to the device taught in the former publication, the terminal voltage of the battery is sensed, and the field current of the dynamo is controlled with reference to the sensor output so at to reduce the physical demands on the rider and to stabilize lamp brightness. According to the device taught in the latter publication, a charge capacitor is provided so that electrical power may be supplied to the lamp by the charge capacitor during times of low power generation by the dynamo.
Newer bicycles are often equipped with additional devices driven by the dynamo, such as actuators for changing speed in electrically-powered gear shifting systems, actuators for regulating damper force in electrically-powered suspensions, and indicator backlights for cycle computers (such devices are hereinafter referred to as xe2x80x9celectrically-powered unitsxe2x80x9d). Such electrically powered units experience unstable operation when drive voltage goes below a certain predetermined voltage. For example, if an actuator consists of a motor, lower drive voltage may result in problems such as slow speed or an inability to operate at normal speed; in an electrically-powered gear shifting system coming to a halt in the middle of a shift operation; or in the actuator in an electrically-powered suspension suddenly becoming non-operational. When an electrically powered unit employs a microprocessor, errors in operation may result. In the case of an indicator backlight, visibility may be impaired due to insufficient illumination.
For the same given dynamo speed, voltage is lower when the lamp is on than when it is off, and thus particularly in bicycles equipped with electrically-powered units of the kind described above, it is crucial to achieve stable charged voltage. However, conventional devices like those described above, while capable of supplying stable electric power to a lamp, are not capable of supplying stable electric power to the other electrically powered units. This results in a need to provide a step-up transformer or step-up circuit in order to provide stable power supply to electrically-powered units while keeping the lamp lit, which results in the problem of higher device cost.
The present invention is directed to a dynamo control circuit for a bicycle wherein lamp operation is controlled to reduce the load on the battery. In one embodiment of the present invention, a bicycle charge control circuit for receiving electric power from a bicycle dynamo and for controlling the operation of a lamp and a charging circuit includes a lamp switch for selectively providing power from the dynamo to the lamp, a battery charged by the dynamo, and a lamp control circuit operatively coupled to the first lamp switch and to the battery to control the first lamp switch to intermittently supply power to the lamp when the battery voltage is below a selected value. In a more specific embodiment, a rectifier rectifies power from the dynamo to the battery, and the lamp control circuit controls the lamp switch to supply power to the lamp at intervals approximately equal to half-cycles of the output voltage of the dynamo. The lamp control circuit allows full power to be communicated to the lamp when the battery voltage is above the selected value.